An Inductive Debris Monitor (IDM) detects and classifies particles which are present in a passageway of a fluid wetted system. In this respect, the IDM is especially, though not exclusively, concerned with the detection of metal chips or other particles, in an oil or other fluid line of a combustion engine.
The detected chips are categorized by size, rate of occurrence and whether they are magnetic or non-magnetic. This categorization of particles present in a fluid passageway provides a useful check on the status of the engine, and enables an early warning and identification of defects or malfunctions in an engine before those defects or malfunctions have serious consequences.
A prior art IDM is illustrated in FIGS. 1-3 and is identified generally by the numeral 10. The prior art IDM 10 comprises an inductive sensor 12 and an electronic circuit 14. The prior art inductive sensor 12 is placed along a fluid passageway 16 in a fluid wetted system, and connects to a transformer bridge 18 in the prior art electronic circuit 14. The transformer bridge 18 connects to a voltage control oscillator 20, a voltage controlled resistor 22, a pre-amplifier 24, an active amplifier 25 and a reactive error amplifier 26.
In use, alternating electric current is applied to the prior art inductive sensor 12 from the electronic circuit 14. The alternating current, tuned at the sensor resonant frequency, provides an electromagnetic field within the portion of the tubing 16 surrounded by the inductive sensor 12. This electromagnetic field is then monitored by the prior art electronic circuit 14 for any chip particles which may be present in a fluid flow contained within the portion of the tubing 16 being monitored by the prior art IDM 10. Chip particles that pass through the portion of the tubing 16 being monitored, cause a change in the inductance of the prior art inductive sensor 12. As shown by line "A" in FIG. 2, changes in phase angle relationships denote magnetic characteristics, while quantitative changes in the sensor inductance, as shown by line "B" with respect to voltage and time denote particle size. However, the transformer bridge 18 of FIG. 3 and other parts of the prior art electronic circuit 14 were prone to cause additional uncompensated phase shifts when correlated to temperature environments. Also, the exposure to high temperature environments quite often resulted in a reduction of sensor sensitivity. Further, the inductive sensor 12 of the prior art IDM 10 often had a low signal to noise ratio for small particles (e.g. less than 15 mil) caused by the spaced-apart relationship of the loops of the inductive coil 12 which surrounded the fluid passageway 16.
Another prior art IDM is shown in U.S. Pat. No. 4,926,120 which is issued to Veronesi. The prior art IDM of U.S. Pat. No. 4,926,120 includes a probe member which is illustrated in FIG. 4 herein, and which is identified by the numeral 28. The prior art probe member 28 is formed from a planar sheet 30 of a highly conductive metal which is wrapped partly around the outer circumference of a tube 31 containing the fluid flow to be monitored for chip particle detection. End portions 32 and 34 of the prior art probe 28 are bent to extend away from the tube 31 and are in spaced parallel relationship to one another. Capacitors 36 are interposed between the spaced end portions 32 and 34 of the probe member 28. The probe member 28 of FIG. 4 is advantageous over the coil 12 of FIG. 1, in that the probe member 28 of FIG. 4 reduces the signal-to-noise ratio. However, the probe member 28 of FIG. 4 has an undesirably low sensitivity, particularly for smaller particles. Further, the probe member 28 of FIG. 4 does not overcome the poor performance of the circuit 14 of FIG. 2 in high temperature environments.
Accordingly, it is an object of the present invention to avoid the disadvantages of the prior art.
More particularly, it is an object of the present invention to provide an inductive debris monitor which provides an increased sensitivity to chip particles having ferromagnetic and non-ferromagnetic characteristics.
Still another object of the present invention is to provide an inductive debris monitor which has lower loss of sensitivity compared to the prior art when subject to high temperature environments.